

<!DOCTYPE html>
<!--[if IE 8]><html class="no-js lt-ie9" lang="en" > <![endif]-->
<!--[if gt IE 8]><!--> <html class="no-js" lang="en" > <!--<![endif]-->
<head>
  <meta charset="utf-8">
  
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  
  <title>2.11 删除字符串中不需要的字符 &mdash; python3-cookbook 3.0.0 documentation</title>
  

  
  
  
  

  

  
  
    

  

  <link rel="stylesheet" href="../_static/css/theme.css" type="text/css" />
  <link rel="stylesheet" href="../_static/pygments.css" type="text/css" />
    <link rel="index" title="Index" href="../genindex.html" />
    <link rel="search" title="Search" href="../search.html" />
    <link rel="next" title="2.12 审查清理文本字符串" href="p12_sanitizing_clean_up_text.html" />
    <link rel="prev" title="2.10 在正则式中使用Unicode" href="p10_work_with_unicode_in_regexp.html" /> 

  
  <script src="../_static/js/modernizr.min.js"></script>

</head>

<body class="wy-body-for-nav">

   
  <div class="wy-grid-for-nav">

    
    <nav data-toggle="wy-nav-shift" class="wy-nav-side">
      <div class="wy-side-scroll">
        <div class="wy-side-nav-search">
          

          
            <a href="../index.html" class="icon icon-home"> python3-cookbook
          

          
          </a>

          
            
            
              <div class="version">
                3.0
              </div>
            
          

          
<div role="search">
  <form id="rtd-search-form" class="wy-form" action="../search.html" method="get">
    <input type="text" name="q" placeholder="Search docs" />
    <input type="hidden" name="check_keywords" value="yes" />
    <input type="hidden" name="area" value="default" />
  </form>
</div>

          
        </div>

        <div class="wy-menu wy-menu-vertical" data-spy="affix" role="navigation" aria-label="main navigation">
          
            
            
              
            
            
              <ul class="current">
<li class="toctree-l1"><a class="reference internal" href="../chapters/p01_data_structures_algorithms.html">第一章：数据结构和算法</a></li>
<li class="toctree-l1 current"><a class="reference internal" href="../chapters/p02_strings_and_text.html">第二章：字符串和文本</a><ul class="current">
<li class="toctree-l2"><a class="reference internal" href="p01_split_string_on_multiple_delimiters.html">2.1 使用多个界定符分割字符串</a></li>
<li class="toctree-l2"><a class="reference internal" href="p02_match_text_at_start_end.html">2.2 字符串开头或结尾匹配</a></li>
<li class="toctree-l2"><a class="reference internal" href="p03_match_strings_with_shell_wildcard.html">2.3 用Shell通配符匹配字符串</a></li>
<li class="toctree-l2"><a class="reference internal" href="p04_match_and_search_text.html">2.4 字符串匹配和搜索</a></li>
<li class="toctree-l2"><a class="reference internal" href="p05_search_and_replace_text.html">2.5 字符串搜索和替换</a></li>
<li class="toctree-l2"><a class="reference internal" href="p06_search_replace_case_insensitive.html">2.6 字符串忽略大小写的搜索替换</a></li>
<li class="toctree-l2"><a class="reference internal" href="p07_specify_regexp_for_shortest_match.html">2.7 最短匹配模式</a></li>
<li class="toctree-l2"><a class="reference internal" href="p08_regexp_for_multiline_partterns.html">2.8 多行匹配模式</a></li>
<li class="toctree-l2"><a class="reference internal" href="p09_normalize_unicode_text_to_regexp.html">2.9 将Unicode文本标准化</a></li>
<li class="toctree-l2"><a class="reference internal" href="p10_work_with_unicode_in_regexp.html">2.10 在正则式中使用Unicode</a></li>
<li class="toctree-l2 current"><a class="current reference internal" href="#">2.11 删除字符串中不需要的字符</a><ul>
<li class="toctree-l3"><a class="reference internal" href="#id2">问题</a></li>
<li class="toctree-l3"><a class="reference internal" href="#id3">解决方案</a></li>
<li class="toctree-l3"><a class="reference internal" href="#id4">讨论</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="p12_sanitizing_clean_up_text.html">2.12 审查清理文本字符串</a></li>
<li class="toctree-l2"><a class="reference internal" href="p13_aligning_text_strings.html">2.13 字符串对齐</a></li>
<li class="toctree-l2"><a class="reference internal" href="p14_combine_and_concatenate_strings.html">2.14 合并拼接字符串</a></li>
<li class="toctree-l2"><a class="reference internal" href="p15_interpolating_variables_in_strings.html">2.15 字符串中插入变量</a></li>
<li class="toctree-l2"><a class="reference internal" href="p16_reformat_text_to_fixed_number_columns.html">2.16 以指定列宽格式化字符串</a></li>
<li class="toctree-l2"><a class="reference internal" href="p17_handle_html_xml_in_text.html">2.17 在字符串中处理html和xml</a></li>
<li class="toctree-l2"><a class="reference internal" href="p18_tokenizing_text.html">2.18 字符串令牌解析</a></li>
<li class="toctree-l2"><a class="reference internal" href="p19_writing_recursive_descent_parser.html">2.19 实现一个简单的递归下降分析器</a></li>
<li class="toctree-l2"><a class="reference internal" href="p20_perform_text_operations_on_byte_string.html">2.20 字节字符串上的字符串操作</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="../aboutme.html">关于</a></li>
</ul>

            
          
        </div>
      </div>
    </nav>

    <section data-toggle="wy-nav-shift" class="wy-nav-content-wrap">

      
      <nav class="wy-nav-top" aria-label="top navigation">
        
          <i data-toggle="wy-nav-top" class="fa fa-bars"></i>
          <a href="../index.html">python3-cookbook</a>
        
      </nav>


      <div class="wy-nav-content">
        
        <div class="rst-content">
        
          















<div role="navigation" aria-label="breadcrumbs navigation">

  <ul class="wy-breadcrumbs">
    
      <li><a href="../index.html">Docs</a> &raquo;</li>
        
          <li><a href="../chapters/p02_strings_and_text.html">第二章：字符串和文本</a> &raquo;</li>
        
      <li>2.11 删除字符串中不需要的字符</li>
    
    
      <li class="wy-breadcrumbs-aside">
        
            
            <a href="../_sources/c02/p11_strip_unwanted_characters.rst.txt" rel="nofollow"> View page source</a>
          
        
      </li>
    
  </ul>

  
  <hr/>
</div>
          <div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article">
           <div itemprop="articleBody">
            
  <div class="section" id="id1">
<h1>2.11 删除字符串中不需要的字符<a class="headerlink" href="#id1" title="Permalink to this headline">¶</a></h1>
<div class="section" id="id2">
<h2>问题<a class="headerlink" href="#id2" title="Permalink to this headline">¶</a></h2>
<p>你想去掉文本字符串开头，结尾或者中间不想要的字符，比如空白。</p>
</div>
<div class="section" id="id3">
<h2>解决方案<a class="headerlink" href="#id3" title="Permalink to this headline">¶</a></h2>
<p><code class="docutils literal notranslate"><span class="pre">strip()</span></code> 方法能用于删除开始或结尾的字符。 <code class="docutils literal notranslate"><span class="pre">lstrip()</span></code> 和 <code class="docutils literal notranslate"><span class="pre">rstrip()</span></code> 分别从左和从右执行删除操作。
默认情况下，这些方法会去除空白字符，但是你也可以指定其他字符。比如：</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="c1"># Whitespace stripping</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">s</span> <span class="o">=</span> <span class="s1">&#39; hello world </span><span class="se">\n</span><span class="s1">&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">s</span><span class="o">.</span><span class="n">strip</span><span class="p">()</span>
<span class="go">&#39;hello world&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">s</span><span class="o">.</span><span class="n">lstrip</span><span class="p">()</span>
<span class="go">&#39;hello world \n&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">s</span><span class="o">.</span><span class="n">rstrip</span><span class="p">()</span>
<span class="go">&#39; hello world&#39;</span>
<span class="go">&gt;&gt;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="c1"># Character stripping</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">t</span> <span class="o">=</span> <span class="s1">&#39;-----hello=====&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">t</span><span class="o">.</span><span class="n">lstrip</span><span class="p">(</span><span class="s1">&#39;-&#39;</span><span class="p">)</span>
<span class="go">&#39;hello=====&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">t</span><span class="o">.</span><span class="n">strip</span><span class="p">(</span><span class="s1">&#39;-=&#39;</span><span class="p">)</span>
<span class="go">&#39;hello&#39;</span>
<span class="go">&gt;&gt;&gt;</span>
</pre></div>
</div>
</div>
<div class="section" id="id4">
<h2>讨论<a class="headerlink" href="#id4" title="Permalink to this headline">¶</a></h2>
<p>这些 <code class="docutils literal notranslate"><span class="pre">strip()</span></code> 方法在读取和清理数据以备后续处理的时候是经常会被用到的。
比如，你可以用它们来去掉空格，引号和完成其他任务。</p>
<p>但是需要注意的是去除操作不会对字符串的中间的文本产生任何影响。比如：</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">s</span> <span class="o">=</span> <span class="s1">&#39; hello     world </span><span class="se">\n</span><span class="s1">&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">s</span> <span class="o">=</span> <span class="n">s</span><span class="o">.</span><span class="n">strip</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">s</span>
<span class="go">&#39;hello     world&#39;</span>
<span class="go">&gt;&gt;&gt;</span>
</pre></div>
</div>
<p>如果你想处理中间的空格，那么你需要求助其他技术。比如使用 <code class="docutils literal notranslate"><span class="pre">replace()</span></code> 方法或者是用正则表达式替换。示例如下：</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">s</span><span class="o">.</span><span class="n">replace</span><span class="p">(</span><span class="s1">&#39; &#39;</span><span class="p">,</span> <span class="s1">&#39;&#39;</span><span class="p">)</span>
<span class="go">&#39;helloworld&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span> <span class="nn">re</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="s1">&#39;\s+&#39;</span><span class="p">,</span> <span class="s1">&#39; &#39;</span><span class="p">,</span> <span class="n">s</span><span class="p">)</span>
<span class="go">&#39;hello world&#39;</span>
<span class="go">&gt;&gt;&gt;</span>
</pre></div>
</div>
<p>通常情况下你想将字符串 <code class="docutils literal notranslate"><span class="pre">strip</span></code> 操作和其他迭代操作相结合，比如从文件中读取多行数据。
如果是这样的话，那么生成器表达式就可以大显身手了。比如：</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="n">filename</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
    <span class="n">lines</span> <span class="o">=</span> <span class="p">(</span><span class="n">line</span><span class="o">.</span><span class="n">strip</span><span class="p">()</span> <span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">f</span><span class="p">)</span>
    <span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">lines</span><span class="p">:</span>
        <span class="k">print</span><span class="p">(</span><span class="n">line</span><span class="p">)</span>
</pre></div>
</div>
<p>在这里，表达式 <code class="docutils literal notranslate"><span class="pre">lines</span> <span class="pre">=</span> <span class="pre">(line.strip()</span> <span class="pre">for</span> <span class="pre">line</span> <span class="pre">in</span> <span class="pre">f)</span></code> 执行数据转换操作。
这种方式非常高效，因为它不需要预先读取所有数据放到一个临时的列表中去。
它仅仅只是创建一个生成器，并且每次返回行之前会先执行 <code class="docutils literal notranslate"><span class="pre">strip</span></code> 操作。</p>
<p>对于更高阶的strip，你可能需要使用 <code class="docutils literal notranslate"><span class="pre">translate()</span></code> 方法。请参阅下一节了解更多关于字符串清理的内容。</p>
</div>
</div>


           </div>
           
          </div>
          <footer>
  
    <div class="rst-footer-buttons" role="navigation" aria-label="footer navigation">
      
        <a href="p12_sanitizing_clean_up_text.html" class="btn btn-neutral float-right" title="2.12 审查清理文本字符串" accesskey="n" rel="next">Next <span class="fa fa-arrow-circle-right"></span></a>
      
      
        <a href="p10_work_with_unicode_in_regexp.html" class="btn btn-neutral" title="2.10 在正则式中使用Unicode" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left"></span> Previous</a>
      
    </div>
  

  <hr/>

  <div role="contentinfo">
    <p>
        &copy; Copyright 2017, 熊能.

    </p>
  </div>
  Built with <a href="http://sphinx-doc.org/">Sphinx</a> using a <a href="https://github.com/rtfd/sphinx_rtd_theme">theme</a> provided by <a href="https://readthedocs.org">Read the Docs</a>. 

</footer>

        </div>
      </div>

    </section>

  </div>
  


  

    <script type="text/javascript">
        var DOCUMENTATION_OPTIONS = {
            URL_ROOT:'../',
            VERSION:'3.0.0',
            LANGUAGE:'None',
            COLLAPSE_INDEX:false,
            FILE_SUFFIX:'.html',
            HAS_SOURCE:  true,
            SOURCELINK_SUFFIX: '.txt'
        };
    </script>
      <script type="text/javascript" src="../_static/jquery.js"></script>
      <script type="text/javascript" src="../_static/underscore.js"></script>
      <script type="text/javascript" src="../_static/doctools.js"></script>

  

  <script type="text/javascript" src="../_static/js/theme.js"></script>

  <script type="text/javascript">
      jQuery(function () {
          SphinxRtdTheme.Navigation.enable(true);
      });
  </script> 

</body>
</html>